This invention relates to a jet propulsion system for a watercraft and more particularly to an improved device for minimizing the sound generated by the jet propulsion unit and also improving the performance of the engine and permitting lower idle speeds without inhibiting the operation of the engine.
Jet propulsion units are quite popular in connection with the propulsion of watercraft and especially a particular type of watercraft referred to as a xe2x80x9cpersonal watercraftxe2x80x9d. These types of watercraft generally are designed to be operated by a rider who may carry no more than one to three additional passengers. Frequently these passengers are seated in straddle, tandem fashion on a longitudinally extending seat that is formed at the rear of the watercraft with the propulsion unit being disposed beneath the seat.
One problem particular with this type of construction can be best understood by reference to FIG. 1, which shows a prior art type of jet propulsion unit commonly utilized in these types of watercraft. The watercraft has a hull portion, indicated by the reference numeral 11 that defines a tunnel in which the jet propulsion unit outer housing, indicated generally by the reference numeral 12, is positioned. In this particular construction, the jet propulsion unit outer housing 12 is disposed above a ride plate 13 that may be affixed to the underside of the hull portion 11 in a suitable manner.
The jet propulsion unit outer housing 12 defines an impeller portion 14 that is disposed forwardly adjacent a bulkhead 15 that separates a tunnel area 16 in which the jet propulsion unit outer housing 12 is positioned from the engine compartment of the watercraft and which is positioned beneath its seat.
An impeller 17 is rotatably journalled in the impeller housing 14 and draws water through a water inlet passage 18. The water inlet passage 18 may be formed in any of a variety of manners and includes a downwardly facing inlet opening 19 through which water is drawn by the impeller 17.
The impeller 17 has affixed to it an impeller shaft 21, which extends forwardly through the bulkhead 15 and into the engine compartment for coupling to the powering prime mover in any known or suitable manner known in the prior art.
The pumped water is then discharged through a steering nozzle 22 that cooperates with a discharge nozzle 23 of the outer housing assembly 12. The steering nozzle 22 is pivotally supported for steering movement relative to the discharge nozzle 23 about a vertically extending axis by a pivot pin 24. By changing the direction of the steering nozzle 22, the associated watercraft is steered in a manner well known in this art.
In addition, a reverse thrust bucket 25 may be mounted at the discharge end of the steering nozzle 22 and in its illustrated position redirects the water flow forwardly so as to cause reverse operation of the associated watercraft. The reverse thrust bucket 25 is supported on the steering nozzle 22 by a further pivot pin 26 and is operated by a bucket control 27 so as to permit forward motion by pivoting the reverse thrust bucket 25 upwardly so that the water discharged from the steering nozzle 22 can go rearwardly.
As may be seen, the water inlet passage 18 curves upwardly from the inlet opening 19 and directly registered with the impeller housing 14 in close proximity to the impeller 17. It has been found that this causes pulsations in the water that is transmitted back through the forward wall of the bulkhead 15 and can create unpleasant vibrations in the watercraft and sounds that are undesirable.
It is, therefore, a first principal feature of this invention to provide an improved and low cost jet propulsion unit for a personal watercraft that avoids these pulsations.
It is a further object of this invention to provide an arrangement for utilizing this feature in conjunction with conventional type jet pumps so as to not require a redesign in either the hull or the jet pump in order to use the feature of the invention.
Another problem with this type of personal watercraft is the effect of noise and vibrations in the exhaust system. Generally, these types of watercraft employ a water trap device which is interposed in the exhaust system and which is designed so as to permit the cooling water from the engine to be mixed with the exhaust gases and provide silencing while reducing the likelihood that water can flow to the engine combustion chambers through the exhaust system.
As a result, these water trap devices are generally positioned rearwardly from the engine and constantly operate with a level of water within them. The exhaust gases must overcome the pressure of this head of water in order to exit the watercraft and this can cause excessive back pressure at idle. Thus, it is a common practice to utilize an accelerated idle speed to prevent stalling or uneven operation.
It is, therefore, a further object to this invention to provide an improved exhaust system for a watercraft that incorporates a water trap and wherein the idle exhaust gases can be discharged independently of the backpressure of water in the water trap.
A first feature of this invention is adapted to be embodied in a jet propulsion system for a watercraft that includes an outer housing having an impeller portion in which an impeller is rotatably journalled and a discharge nozzle portion rearwardly of it though which the water pumped by the impeller is discharged for propelling the associated watercraft. A water inlet assembly is provided that has a downwardly facing water inlet opening through which water may be drawn and curved discharged path that curves upwardly toward the axis of rotation of the impeller. A silencing portion is interposed between the water inlet portion and the impeller housing portion and has a shape that constitutes generally an extension of the opening of the inlet to the impeller housing so as to isolate the pulsations generated by the impeller from the water inlet portion.
In accordance with another feature of this invention, the extension portion can be formed at least in part from an elastomeric material to provide additional damping characteristics.
A propulsion system for a watercraft embodying another principal feature of the invention includes an internal combustion engine that powers a propulsion device and which has an exhaust system that includes a water trap device. The exhaust system further includes an exhaust conduit that conveys exhaust gases from the engine as an inlet to the water trap device. The water trap device communicates with an exhaust discharge for discharging the exhaust gases from the water trap device. At least one of the inlet or discharge portions of the water trap device is designed so as to be at least partially submerged in cooling water that is discharged into the engine exhaust system. This submersions exist under at least some running conditions of the watercraft. The exhaust system further includes a restricted exhaust discharge conduit that extends from the exhaust system upstream of the water trap device and discharges directly to the atmosphere independently of the water trap device.